Secondary battery, electronic device, and method for manufacturing secondary battery

Abstract

The invention relates to a secondary battery, electronic equipment and a manufacturing method of the secondary battery, the secondary battery comprises an electrode assembly, and the electrode assembly comprises a negative plate, a positive plate and a diaphragm. The positive plate comprises a single-sided positive plate arranged on the outermost layer of the electrode assembly in the first direction, and the single-sided positive plate comprises a first positive current collector and a first positive active layer. The first positive current collector comprises a first polymer layer and a first metal layer. First conductive pieces are welded on two opposite surfaces of the second part of the first positive current collector, and a first welding area is formed; the diaphragm comprises a first diaphragm arranged between the single-sided positive plate and the negative plate, a first insulating layer is arranged on the surface, facing the single-sided positive plate, of the first diaphragm, the projection of the first insulating layer on the single-sided positive plate covers the first welding area, the first insulating layer exceeds one side of the first conductive part in the third direction, and the exceeding length is 0.5 mm to 3 mm. According to the secondary battery and the electronic equipment, the problem of short circuit between the positive electrode current collector and the negative electrode active material layer can be solved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery, an electronic device, and a method for manufacturing a secondary battery. Background Art

[0002] As the power source of electronic devices, secondary batteries are the key to ensuring the normal use of electronic devices. The current collector is an important component of the secondary battery. It not only provides support for the active material layer, but also collects the current generated by the active material layer for external output. Therefore, the current collector has an important influence on the performance of the electrode plate and the electrochemical device. However, the current collector is prone to short circuit when it comes into contact with the active material of opposite polarity. Summary of the invention

[0003] The inventor of the present application has found that in order to improve the energy density of existing secondary batteries, composite current collectors (composite structures of metal-polymer-metal) are usually used. Composite current collectors use polymers as the mechanical performance process skeleton, which can make the metal layer thinner. The current collector needs to be connected to the pole ear to transfer the current to the outside, but conventional ultrasonic welding cannot directly connect the pole ear and the composite current collector together (easy to be cold welded or over-welded). At present, the composite current collector is mainly placed in the middle of two layers of metal foil by roller welding, and then welded to the pole ear by the metal foil, so as to realize the connection between the composite current collector and the pole ear, which can improve the reliability of welding and reduce the welding resistance. The composite current collector needs to leave an empty foil section without an active material layer for metal foil welding. However, since the negative active material layer of the negative electrode sheet usually needs to exceed the positive active material layer of the positive electrode sheet, the empty foil area of ​​the positive composite current collector of the positive electrode sheet corresponds to the negative active material layer. After two layers of metal foil are welded in the empty foil area of ​​the positive composite current collector, the metal burrs in the welding area can easily pierce the diaphragm and form a short circuit with the negative active material layer on the opposite side, thereby reducing the safety performance of the secondary battery.

[0004] The purpose of the present application is to provide a secondary battery, an electronic device and a method for manufacturing a secondary battery, aiming to improve the problem of short circuit between a positive electrode current collector and a negative electrode active material layer.

[0005] According to the first aspect of the present application, a secondary battery is provided, comprising an electrode assembly, the electrode assembly comprising a negative electrode sheet, a positive electrode sheet and a separator, the negative electrode sheets and the positive electrode sheets are alternately stacked along a first direction, and a separator is arranged between adjacent negative electrode sheets and positive electrode sheets. The positive electrode sheet comprises a single-sided positive electrode sheet, the outermost electrode sheet of the electrode assembly along the first direction is a single-sided positive electrode sheet, the single-sided positive electrode sheet comprises a first positive electrode collector and a first positive electrode active layer, the first positive electrode collector comprises a first part and a second part connected in sequence along a second direction, the surface of the first part facing the negative electrode sheet is provided with the first positive electrode active layer, and the first positive electrode active layer is not provided on the two opposite surfaces of the second part along the first direction. The first positive electrode collector comprises a first metal layer and a first polymer layer, and the first metal layer is provided on the two opposite surfaces of the first polymer layer along the first direction. The first conductive member is welded to the two opposite surfaces of the second part along the first direction, and a first welding area is formed. The first conductive member protrudes from the second part along the second direction. The diaphragm includes a first diaphragm, the first diaphragm is arranged between the single-sided positive electrode sheet and the adjacent negative electrode sheet, the first diaphragm is provided with a first insulating layer on the surface facing the single-sided positive electrode sheet, and the projection of the first insulating layer on the surface of the single-sided positive electrode sheet along the first direction covers the first welding area. Along the third direction, the length of the first insulating layer is L1, the width of the first conductive member is L2, 1mm≤L1-L2≤6mm, the first insulating layer exceeds one side of the first conductive member, and the exceeding length is 0.5mm to 3mm, and the first direction, the second direction and the third direction are perpendicular to each other.

[0006] In the above technical solution, by setting the outermost electrode sheet of the electrode assembly along the first direction as a single-sided positive electrode sheet, the possibility of damage to the shell of the outer packaging can be reduced. This is because if the outermost electrode sheet of the electrode assembly adopts a single-sided negative electrode sheet, the metal copper of the current collector of the single-sided negative electrode sheet is easy to react electrochemically with the metal aluminum of the shell, thereby causing damage to the shell. The first positive active layer is set on the surface of the first positive current collector of the single-sided positive electrode sheet facing the negative electrode sheet, which can improve the utilization rate of the positive active material of the single-sided positive electrode sheet, thereby improving the energy density. By setting the first positive current collector to a structure of two layers of first metal layers sandwiching the first polymer layer, the first metal layer can be made thinner, thereby improving the energy density of the secondary battery. By welding the first conductive member on both opposite surfaces of the second part of the first positive current collector along the first direction, it is convenient to connect the positive electrode tab to the first positive current collector through the first conductive member. By setting a first insulating layer on the surface of the first diaphragm facing the single-sided positive electrode sheet, and the projection of the first insulating layer on the surface of the single-sided positive electrode sheet along the first direction covers the first welding area, so that the first insulating layer can block the metal burrs of the first welding area, thereby reducing the possibility that the metal burrs of the first welding area pierce the first diaphragm and form a short circuit with the negative active material layer of the opposite negative electrode sheet. In addition, since the first insulating layer is only set on the first diaphragm of the outermost layer of the electrode assembly, the electrode assembly can first stack the pole pieces of the middle layer during the preparation process, and then set the first insulating layer on the outermost first diaphragm, and then stack the single-sided positive electrode sheet, without first bonding the diaphragm to the insulating layer and then rolling it up and then stacking the pole pieces, thereby reducing the possibility that the diaphragm is difficult to roll up after being bonded to the insulating layer, and reducing the possibility that the diaphragm will bulge and tear after being rolled up. By limiting 1mm≤L1-L2, the first insulating layer can better block the metal burrs of the first welding area. Since the first insulating layer is too long and is easy to fold, thus affecting its effect of shielding the first welding area, the length of the first insulating layer is limited to L1-L2≤6mm so that the length of the first insulating layer will not be too long, thereby reducing the possibility of the first insulating layer folding, thereby further increasing the possibility of the first insulating layer shielding the metal burrs of the first welding area. The first insulating layer extends beyond one side of the first conductive part along the third direction, and the length of the excess is 0.5mm to 3mm, which means that when the first insulating layer extends beyond either side of the first conductive part, the length of the single-side excess is 0.5mm to 3mm. By limiting the first insulating layer to extend beyond one side of the first conductive part along the third direction, and the length of the excess is 0.5mm to 3mm, the first insulating layer can further better shield the metal burrs of the first welding area, and at the same time, the length of the first insulating layer will not be too long, so it is not easy to fold.

[0007] In some preferred embodiments, along the third direction, the first insulating layer extends beyond both sides of the first conductive member, and the length beyond either side of the first conductive member is 0.5 mm to 3 mm, which further enables the first insulating layer to better shield the metal burrs of the first welding area. At the same time, the length of the first insulating layer will not be too long, making it difficult to fold.

[0008] In some preferred embodiments, along the third direction, the first conductive member includes a first bend and a first main body connected in sequence, and the first insulating layer exceeds the side of the first bend away from the first main body, and the length of the excess is 0.5mm to 3mm. Torque will be formed in the process of die-cutting the first conductive member, and the first bend can buffer the torque to reduce the possibility of the first positive electrode current collector being torn due to the torque. Since the length of the first insulating layer is limited by the processing accuracy, by limiting the first insulating layer to exceed the side of the first bend away from the first main body, and the excess length is not less than 0.5mm, the first insulating layer can be given a larger processing accuracy space while satisfying the first insulating layer can better block the metal burrs of the first welding area. By limiting the first insulating layer to exceed the side of the first bend away from the first main body, and the excess length is not more than 3mm, the possibility of the first insulating layer being too long and easy to fold can be reduced, and the possibility of the first insulating layer being too long to lose more energy density of the secondary battery can be reduced.

[0009] In some preferred embodiments, the first conductive member includes a second bend, and along the third direction, the second bend is connected to the side of the first main body away from the first bend, and the first insulating layer exceeds the side of the second bend away from the first main body, and the length of the excess is 0.5mm to 3mm. The second bend can buffer the torque force of the die-cutting process to further reduce the possibility of the first positive electrode current collector being torn due to the torque force. By limiting the first insulating layer to exceed the side of the second bend away from the first main body, and the excess length is not less than 0.5mm, the first insulating layer can be given a larger processing accuracy space while satisfying that the first insulating layer can better shield the metal burrs of the first welding area. By limiting the first insulating layer to exceed the side of the second bend away from the first main body, and the excess length is not more than 3mm, the possibility of the first insulating layer being too long and easy to fold can be reduced, and the possibility of the first insulating layer being too long to lose more energy density of the secondary battery can be reduced.

[0010] In some preferred embodiments, along the second direction, the width of the first insulating layer is W1, 1.4mm≤W1≤4mm, so that the first insulating layer can well shield the metal burrs in the first welding area while not being too wide to excessively consume the energy density of the secondary battery.

[0011] In some preferred embodiments, along the first direction, the thickness of the first insulating layer is H1, 10 μm ≤ H1 ≤ 20 μm, so that the first insulating layer is not too thick while meeting good anti-puncture performance, and does not excessively lose the energy density of the secondary battery.

[0012] In some preferred embodiments, the first insulating layer includes a first adhesive layer and a first substrate layer. Along the first direction, the first adhesive layer is provided with the first substrate layer on one surface, and the other surface of the first adhesive layer away from the first substrate layer is provided on the first diaphragm. The thickness of the first adhesive layer is H2, 2μm≤H2≤7μm, and the thickness of the first substrate layer is H3, 8μm≤H3≤13μm. The first adhesive layer can improve the adhesion of the first insulating layer to the first diaphragm, and the first substrate layer can improve the puncture resistance of the first insulating layer. By limiting 2μm≤H2≤7μm, the first adhesive layer has a better bonding effect, while the first adhesive layer is not too thick, so as not to excessively reduce the energy density of the secondary battery. By limiting 8μm≤H3≤13μm, the first substrate layer has a better insulation effect, while the first substrate layer is not too thick, so as not to excessively reduce the energy density of the secondary battery.

[0013] In some preferred embodiments, along the second direction, the width of the first welding area is W2, 0.8mm≤W2≤3mm. By limiting 0.8mm≤W2, the first welding area has good welding strength, so that the first conductive member can be firmly attached to the first positive electrode current collector. Since the first insulating layer needs to shield the first welding area, if the width of the first welding area increases, the width of the corresponding first insulating layer also needs to increase. Therefore, by limiting W2≤3mm, the width of the first welding area will not be too wide, and the width of the first insulating layer will not be too wide, so as not to excessively reduce the energy density of the secondary battery.

[0014] In some preferred embodiments, 6.5 mm ≤ L2 ≤ 15.5 mm, so that the first conductive member and the first positive electrode current collector have a good connection strength, while the first conductive member is not too long, thereby not excessively reducing the energy density of the secondary battery.

[0015] In some preferred embodiments, the negative electrode sheet includes a first negative electrode current collector and a first negative electrode active layer, the first negative electrode current collector is provided with a first negative electrode active layer on at least one surface along the first direction, and the first negative electrode active layer includes a third part and a fourth part connected in sequence along the second direction, the projection of the third part on the surface of the single-sided positive electrode sheet overlaps with the first part, and the projection of the fourth part on the surface of the single-sided positive electrode sheet overlaps with at least part of the second part. Along the second direction, the width of the fourth part is W3, 0.5mm≤W3≤2mm. By limiting 0.5mm≤W3, the first negative electrode active layer can better absorb the lithium ions released by the first positive electrode active layer, reducing the possibility of lithium precipitation on the surface of the first negative electrode active layer. By limiting W3≤2mm, the negative electrode active material of the first negative electrode active layer has a better energy utilization rate without excessively reducing the energy density of the secondary battery.

[0016] In some preferred embodiments, the first diaphragm includes a fifth portion and a sixth portion connected in sequence along the second direction. Along the first direction, the projection of the fifth portion on the surface of the negative electrode sheet overlaps with the first negative electrode active layer. Along the second direction, the sixth portion exceeds the first negative electrode active layer, and the width of the sixth portion is W4, 0.5mm≤W4≤2mm. By limiting 0.5mm≤W4, the sixth portion of the first diaphragm can block the first negative electrode active layer, reducing the possibility of the first negative electrode active layer contacting the first conductive member and short-circuiting. By limiting W4≤2mm, the sixth portion of the first diaphragm will not be too wide, and the energy density of the secondary battery will not be reduced too much.

[0017] In some preferred embodiments, the first positive electrode active layer includes a seventh part and an eighth part, and the eighth part is connected to the side of the seventh part close to the first conductive member along the second direction. Along the first direction, the thickness of the eighth part is less than the thickness of the seventh part, and the projection of the first insulating layer on the surface of the single-sided positive electrode sheet overlaps at least partially with the eighth part. The first positive electrode active layer will form a torque during the cold pressing process. By limiting the thickness of the eighth part of the first positive electrode active layer to be less than the thickness of the seventh part, the thinner eighth part can buffer the torque to reduce the possibility of the first positive current collector being torn due to the torque. Since the eighth part is thin, by limiting the projection of the first insulating layer on the surface of the single-sided positive electrode sheet to overlap at least partially with the eighth part, the thickness of the electrode assembly along the first direction will not be increased too much, and the possibility of the first insulating layer shielding the first welding area can be further increased.

[0018] In some preferred embodiments, the positive electrode sheet includes a double-sided positive electrode sheet, a double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets along the first direction, the double-sided positive electrode sheet includes a second positive electrode collector and a second positive electrode active layer, the second positive electrode collector includes a ninth part and a tenth part connected in sequence along the second direction, the second positive electrode active layer is arranged on both opposite surfaces of the ninth part along the first direction, and the second positive electrode active layer is not arranged on both opposite surfaces of the tenth part along the first direction, the second positive electrode collector includes a second metal layer and a second polymer layer, and the second polymer layer is arranged on both opposite surfaces of the second polymer layer along the first direction. The second conductive member is welded on both opposite surfaces of the tenth part along the first direction to form a second welding area. The diaphragm includes a second diaphragm, a second diaphragm is arranged between the double-sided positive electrode sheet and the negative electrode sheet, a second insulating layer is arranged on a surface of the second diaphragm facing the double-sided positive electrode sheet, and the projection of the second insulating layer on the surface of the double-sided positive electrode sheet along the first direction covers the second welding area. A double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets along the first direction, and a second positive active layer is arranged on both opposite surfaces of the second positive electrode collector of the double-sided positive electrode sheet, so that the number of layers of the second positive electrode collector can be reduced, thereby improving the energy density of the secondary battery. By arranging the second positive electrode collector as a structure in which two layers of second metal layers sandwich a second polymer layer, the second metal layer can be made thinner, thereby improving the energy density of the secondary battery. By welding the second conductive member on both opposite surfaces of the tenth part of the second positive electrode collector along the first direction, it is convenient for the positive electrode tab to be connected to the second positive electrode collector through the second conductive member. By arranging a second insulating layer on a surface of the second diaphragm facing the double-sided positive electrode sheet, and the projection of the second insulating layer on the surface of the double-sided positive electrode sheet along the first direction covers the second welding area, so that the second insulating layer can block the metal burrs of the second welding area, thereby reducing the possibility of the metal burrs of the second welding area piercing the second diaphragm and forming a short circuit with the negative active material layer of the opposite negative electrode sheet.

[0019] In some preferred embodiments, the electrode assembly satisfies at least one of the following conditions: (1) the first metal layer comprises aluminum. (2) the first polymer layer comprises polyolefin. (3) the first conductive member comprises aluminum. (4) the first insulating layer comprises polyolefin.

[0020] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as in any embodiment of the first aspect above.

[0021] In the third aspect, the present application also proposes a method for manufacturing a secondary battery, which is used to prepare a secondary battery as in any embodiment of the first aspect, comprising: providing a negative electrode sheet, a separator and a double-sided positive electrode sheet, and stacking the separator, the negative electrode sheet, the separator and the double-sided positive electrode sheet in sequence along the first direction to form a first component, wherein the outermost electrode sheet of the first component along the first direction is the negative electrode sheet, and the outermost layer of the first component along the first direction is stacked with a first separator. Provide a first insulating layer, and set the first insulating layer on a surface of the first separator of the first component away from the negative electrode sheet to form a second component. Provide a single-sided positive electrode sheet and a first conductive member, and weld the first conductive member to the opposite surfaces of the second part of the first positive electrode collector of the single-sided positive electrode sheet to form a first welding area. Stack the single-sided positive electrode sheet welded with the first conductive member on the opposite surfaces of the second component along the first direction, wherein the projection of the first insulating layer on the surface of the single-sided positive electrode sheet along the first direction covers the first welding area. Through the above-mentioned manufacturing method, when the diaphragm in the middle layer of the electrode assembly is not provided with an insulating layer, there is no need to first bond the diaphragm to the insulating layer and then roll it up and then stack the electrode sheets, thereby reducing the possibility that the diaphragm will be difficult to roll up after being bonded to the insulating layer, and reducing the possibility that the diaphragm will bulge and tear after being rolled up due to the insulation layer being bonded.

[0022] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and unless otherwise stated, the dimensions in the drawings do not constitute proportional limitations.

[0024] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0025] Figure 2 This is a schematic diagram of the structure of the electrode assembly of some embodiments of the present application;

[0026] Figure 3 This is a schematic structural diagram of the first positive electrode current collector of some embodiments of the present application;

[0027] Figure 4 A schematic diagram of the structure of a single-sided positive electrode sheet along a first direction according to some embodiments of the present application;

[0028] Figure 5 A schematic diagram of the structure of the first insulating layer in some embodiments of the present application;

[0029] Figure 6 This is a schematic diagram of the structure of the electrode assembly of some embodiments of the present application;

[0030] Figure 7 This is a schematic structural diagram of the second positive electrode current collector of some embodiments of the present application;

[0031] Figure 8 A schematic diagram of the structure of a double-sided positive electrode sheet along a first direction according to some embodiments of the present application;

[0032] Fig. 9 This is a schematic structural diagram of the second insulating layer of some embodiments of the present application.

[0033] Description of reference numerals:

[0034] 100. Secondary battery;

[0035] 10. Shell;

[0036] 20. Electrode assembly;

[0037] 21, positive electrode sheet; 211, single-sided positive electrode sheet; 2111, first positive electrode current collector; 211a, first part; 211b, second part; 2113, first metal layer; 2114, first polymer layer; 2112, first positive electrode active layer; 211c, seventh part; 211d, eighth part; 212, double-sided positive electrode sheet; 2121, second positive electrode current collector; 212a, ninth part; 212b, tenth part; 2123, second metal layer; 2124, second polymer layer; 2122, second positive electrode active layer;

[0038] 22, negative electrode sheet; 221, first negative electrode current collector; 222, first negative electrode active layer; 222a, third part; 222b, fourth part;

[0039] 23, diaphragm; 231, first diaphragm; 231a, fifth part; 231b, sixth part; 232, second diaphragm;

[0040] 24, first conductive member; 24a, first welding area; 241, first main body; 242, first bending portion; 243, second bending portion;

[0041] 25, first insulating layer; 251, first adhesive layer; 252, first base material layer;

[0042] 26, second conductive member; 26a, second welding area; 261, second main body; 262, third bending portion; 263, fourth bending portion;

[0043] 27, second insulating layer; 271, second adhesive layer; 272, second base material layer;

[0044] X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0046] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0047] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0048] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0049] The term "perpendicular" is used to describe the ideal state between two components. In actual production or use, there may be a state that is approximately perpendicular between the two components. For example, in combination with numerical descriptions, perpendicularity can refer to the angle between two straight lines being between 90±10°, perpendicularity can also refer to the dihedral angle between two planes being between 90°±10°, and perpendicularity can also refer to the angle between a straight line and a plane being between 90±10°. The two components described as "perpendicular" may not be absolute straight lines or planes, but may be roughly straight lines or planes. From a macroscopic perspective, a component can be considered a "straight line" or a "plane" if the overall extension direction is a straight line or a plane.

[0050] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0051] In the first aspect, the embodiment of the present application provides a secondary battery 100, please refer to Figure 1 The secondary battery 100 includes a shell 10 and an electrode assembly 20 . The shell 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte infiltrates the electrode assembly 20 in the shell 10 .

[0052] For the electrode assembly 20, please refer to Figure 2 , Figure 2 The lamination structure of the electrode assembly 20 is shown. The electrode assembly 20 includes a negative electrode sheet 22, a positive electrode sheet 21 and a separator 23. The positive electrode sheet 21 and the negative electrode sheet 22 are alternately stacked along the first direction X. A separator 23 is provided between adjacent positive electrode sheets 21 and negative electrode sheets 22. The separator 23 is used to insulate and separate the positive electrode sheet 21 and the negative electrode sheet 22. In the embodiment of the present application, the electrode assembly 20 is described as a lamination structure as an example. In some other embodiments, the electrode assembly 20 may also be a winding structure. For example, the positive electrode sheet 21, the separator 23 and the negative electrode sheet 22 are sequentially stacked and then wound to form a wound electrode assembly 20.

[0053] For the above-mentioned positive electrode sheet 21, the positive electrode sheet 21 includes a single-sided positive electrode sheet 211, and the outermost electrode sheet of the electrode assembly 20 along the first direction X is a single-sided positive electrode sheet 211, which can reduce the possibility of damage to the outer packaging shell 10. This is because if the outermost electrode sheet of the electrode assembly 20 adopts a single-sided negative electrode sheet, the metal copper of the current collector of the single-sided negative electrode sheet is easy to electrochemically react with the metal aluminum of the shell 10, thereby causing damage to the shell 10. The single-sided positive electrode sheet 211 includes a first positive electrode collector 2111 and a first positive electrode active layer 2112. The first positive electrode collector 2111 includes a first part 211a and a second part 211b connected in sequence along the second direction Y. The second direction Y is perpendicular to the first direction X. The first part 211a is provided with a first positive electrode active layer 2112 on a surface facing the negative electrode sheet 22, and the first positive electrode active layer 2112 is not provided on the two opposite surfaces of the second part 211b along the first direction X. By disposing the first positive active layer 2112 on a surface of the first positive current collector 2111 of the single-sided positive electrode sheet 211 facing the negative electrode sheet 22 , the utilization rate of the positive active material of the single-sided positive electrode sheet 211 can be improved, thereby improving the energy density.

[0054] As for the first positive electrode active layer 2112, the first positive electrode active layer 2112 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first positive electrode active layer 2112 includes a first positive electrode active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated on a surface of the first part 211a of the first positive electrode collector 2111 facing the negative electrode sheet 22, thereby obtaining the first positive electrode active layer 2112. The first positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0055] For the first positive electrode current collector 2111, please refer to Figure 2 and Figure 3The first positive electrode current collector 2111 includes a first metal layer 2113 and a first polymer layer 2114, and the first metal layer 2113 is provided on both opposite surfaces of the first polymer layer 2114 along the first direction X. By setting the first positive electrode current collector 2111 as a structure in which two layers of the first metal layer 2113 sandwich the first polymer layer 2114, the first metal layer 2113 can be made thinner, thereby reducing the metal burrs caused by the mechanical damage of the secondary battery 100, and reducing the mass of the first positive electrode current collector 2111, thereby improving the mass energy density of the secondary battery 100. The first polymer layer 2114, as the main mechanical support layer of the first positive electrode current collector 2111, can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), and the first metal layer 2113 can include at least one of aluminum, copper, nickel, titanium, and silver.

[0056] For the above-mentioned negative electrode sheet 22, the negative electrode sheet 22 includes a first negative electrode current collector 221 and a first negative electrode active layer 222. The first negative electrode current collector 221 is provided with a first negative electrode active layer 222 on at least one surface along the first direction X. The first negative electrode active layer 222 includes a third part 222a and a fourth part 222b connected in sequence along the second direction Y. The projection of the third part 222a on the surface of the single-sided positive electrode sheet 211 overlaps with the first part 211a, and the projection of the fourth part 222b on the surface of the single-sided positive electrode sheet 211 overlaps with at least part of the second part 211b. Along the second direction Y, the width of the fourth part 222b is W3, 0.5mm≤W3≤2mm. By limiting 0.5mm≤W3, the first negative electrode active layer 222 can better absorb the lithium ions released by the first positive electrode active layer 2112, and reduce the possibility of lithium deposition on the surface of the first negative electrode active layer 222. By limiting W3≤2 mm, the negative electrode active material of the first negative electrode active layer 222 has a better energy utilization rate without reducing the energy density of the secondary battery 100 too much.

[0057] For the first negative electrode active layer 222, the first negative electrode active layer 222 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first negative electrode active layer 222 includes a first negative electrode active material, a conductive agent, a binder, etc. The above materials are mixed and stirred evenly and coated on at least one surface of the negative electrode current collector along the first direction X, thereby obtaining the first negative electrode active layer 222. The first negative electrode active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0058] For the first negative electrode current collector 221, the first negative electrode current collector 221 may be a composite current collector (a composite structure of metal-polymer-metal), for example, the first negative electrode current collector 221 includes a polymer layer and a metal layer disposed on two opposite surfaces of the polymer layer, the polymer layer as the main mechanical support layer of the first negative electrode current collector 221, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), the metal layer may include at least one of aluminum, copper, nickel, titanium, and silver, the first negative electrode current collector 221 uses the polymer layer as the main mechanical support layer, the metal layer may be thinned, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100, and reducing the mass of the first negative electrode current collector 221, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the first negative electrode current collector 221 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0059] In some embodiments, the first conductive member 24 is welded to both opposite surfaces of the second portion 211b of the first positive electrode current collector 2111 along the first direction X, and a first welding area 24a is formed. The first conductive member 24 protrudes from the second portion 211b along the second direction Y to facilitate the positive electrode tab to be connected to the first positive electrode current collector 2111 through the first conductive member 24. The first conductive member 24 may include at least one of aluminum, copper, nickel, titanium, and silver. The first positive electrode current collector 2111 is placed between two first conductive members 24 by roller welding to improve the reliability of welding and reduce welding resistance. However, the metal burrs of the first welding area 24a easily pierce the diaphragm 23 and form a short circuit with the first negative electrode active layer 222 on the opposite side, thereby reducing the safety performance of the secondary battery 100.

[0060] There are currently two solutions to the above problem. The first solution is to stick adhesive tape on the first welding area 24a so that the adhesive tape covers the metal burrs of the first welding area 24a to reduce the possibility that the metal burrs of the first welding area 24a pierce the diaphragm 23 and form a short circuit with the first negative electrode active layer 222 on the opposite side. However, the adhesive tape pasting process is cumbersome. Adding the adhesive pasting process to the roller welding process will greatly amplify the process size accuracy error, thereby greatly reducing the manufacturing quality rate of the electrode. In addition, the glue in the adhesive tape has the ability to dissolve the adhesive of the first positive electrode active layer 2112 of the single-sided positive electrode sheet 211, which will cause the positive electrode active material particles of the first positive electrode active layer 2112 near the first conductive member 24 to fall off. In addition, when cutting the electrode, the knife die will adhere to the glue of the adhesive tape, resulting in a poor cutting effect, thereby reducing the manufacturing quality rate of the electrode, and the knife die cleaning frequency needs to be increased, thereby reducing production efficiency. The second solution is to provide a ceramic layer on both opposite surfaces of the second part 211b along the first direction X, and make the ceramic layer between the first positive electrode active layer 2112 and the first conductive member 24 along the second direction Y, so that the first conductive member 24 can extend beyond the first negative electrode active layer 222 along the second direction Y, and the first welding area 24a can extend beyond the first negative electrode active layer 222 along the second direction Y, thereby reducing the possibility that the metal burrs of the first welding area 24a can easily pierce the diaphragm 23 and form a short circuit with the first negative electrode active layer 222 on the opposite side. However, the extended first conductive member 24 will increase the head space of the single-sided positive electrode sheet 211, thereby reducing the energy density of the secondary battery 100.

[0061] To improve the above problems, in the embodiments of this application, please refer to Figure 2 and Figure 4The diaphragm 23 includes a first diaphragm 231, which is arranged between the single-sided positive electrode sheet 211 and the adjacent negative electrode sheet 22. A first insulating layer 25 is arranged on a surface of the first diaphragm 231 facing the single-sided positive electrode sheet 211. The projection of the first insulating layer 25 on the surface of the single-sided positive electrode sheet 211 along the first direction X covers the first welding area 24a, so that the first insulating layer 25 can block the metal burrs of the first welding area 24a, thereby reducing the possibility that the metal burrs of the first welding area 24a pierce the first diaphragm 231 and form a short circuit with the negative active material layer of the opposite negative electrode sheet 22. In addition, since the first insulating layer 25 is only provided on the first diaphragm 231 of the outermost layer of the electrode assembly 20, the electrode assembly 20 can first stack the electrode sheet of the middle layer during the preparation process, and then set the first insulating layer 25 on the first diaphragm 231 of the outermost layer, and then stack the single-sided positive electrode sheet 211, without first bonding the diaphragm 23 to the insulating layer and then rolling it up and then stacking the electrode sheet, thereby reducing the possibility that the diaphragm 23 is difficult to roll up after bonding the insulating layer, and reducing the possibility that the diaphragm 23 will bulge and tear after rolling up the insulating layer. Along the third direction Z, the length of the first insulating layer 25 is L1, the width of the first conductive member 24 is L2, 1mm≤L1-L2≤6mm, the first insulating layer 25 exceeds one side of the first conductive member 24, and the length of the excess is 0.5mm to 3mm, and the third direction Z is perpendicular to the first direction X and the second direction Y respectively. By limiting 1mm≤L1-L2, the first insulating layer 25 can better shield the metal burrs of the first welding area 24a. Since the first insulating layer 25 is too long and is easy to fold, thus affecting its effect of shielding the first welding area 24a, the length of the first insulating layer 25 is limited to L1-L2≤6mm, so that the length of the first insulating layer 25 will not be too long, thereby reducing the possibility of the first insulating layer 25 folding, thereby further increasing the possibility of the first insulating layer 25 shielding the metal burrs of the first welding area 24a. By limiting the first insulating layer 25 to extend beyond one side of the first conductive member 24 along the third direction, and the extended length is 0.5mm to 3mm, the first insulating layer 25 can further better shield the metal burrs of the first welding area 24a, and the length of the first insulating layer 25 will not be too long, so that it is not easy to fold.

[0062] In some embodiments, along the third direction Z, the first insulating layer 25 extends beyond both sides of the first conductive member 24, and the length beyond either side of the first conductive member 24 is 0.5 mm to 3 mm, further enabling the first insulating layer 25 to better shield the metal burrs of the first welding area 24a. At the same time, the length of the first insulating layer 25 is not too long, and thus is not easy to fold.

[0063] In some embodiments, along the third direction Z, the first conductive member 24 includes a first curved portion 242 and a first main body 241 connected in sequence, and the first insulating layer 25 exceeds the side of the first curved portion 242 away from the first main body 241, and the length of the excess is 0.5mm to 3mm. Torque will be formed during the die-cutting process of the first conductive member 24, and the first curved portion 242 can buffer the torque to reduce the possibility of the first positive electrode current collector 2111 being torn due to the torque. Since the length of the first insulating layer 25 is limited by the processing accuracy, by limiting the first insulating layer 25 to exceed the side of the first curved portion 242 away from the first main body 241, and the excess length is not less than 0.5mm, it can be satisfied that the first insulating layer 25 can better shield the metal burrs of the first welding area 24a, while giving the first insulating layer 25 a larger processing accuracy space. By limiting the first insulating layer 25 to extend beyond the first curved portion 242 and away from the first main body portion 241 and with the length of the extension being no greater than 3 mm, the possibility of the first insulating layer 25 being too long and easy to fold can be reduced, as well as the possibility of the first insulating layer 25 being too long and consuming more energy density of the secondary battery 100 can be reduced.

[0064] In some embodiments, the first conductive member 24 includes a second curved portion 243, and along the third direction Z, the second curved portion 243 is connected to the side of the first main body 241 away from the first curved portion 242, and the first insulating layer 25 exceeds the side of the second curved portion 243 away from the first main body 241, and the length of the excess is 0.5mm to 3mm. The second curved portion 243 can buffer the torque force of the die-cutting process to further reduce the possibility of the first positive electrode current collector 2111 being torn due to the torque force. By limiting the first insulating layer 25 to exceed the side of the second curved portion 243 away from the first main body 241, and the length of the excess is not less than 0.5mm, the first insulating layer 25 can be given a larger processing accuracy space while satisfying that the first insulating layer 25 can better shield the metal burrs of the first welding area 24a. By limiting the first insulating layer 25 to extend beyond the second curved portion 243 and away from the first main body portion 241 and the length of the extension is not more than 3 mm, the possibility of the first insulating layer 25 being too long and easy to fold can be reduced, and the possibility of the first insulating layer 25 being too long and consuming more energy density of the secondary battery 100 can be reduced.

[0065] In some embodiments, along the second direction Y, the width of the first insulating layer 25 is W1, 1.4mm≤W1≤4mm, so that the first insulating layer 25 can meet the requirements of being able to better shield the metal burrs of the first welding area 24a while not being too wide to excessively consume the energy density of the secondary battery 100.

[0066] In some embodiments, along the first direction X, the thickness of the first insulating layer 25 is H1, 10 μm≤H1≤20 μm, so that the first insulating layer 25 is not too thick while meeting good anti-puncture performance, thereby not excessively losing the energy density of the secondary battery 100 .

[0067] In some embodiments, please refer to Figure 2 and Figure 5 , the first insulating layer 25 includes a first adhesive layer 251 and a first substrate layer 252. Along the first direction X, the first adhesive layer 251 has a surface provided with the first substrate layer 252, and the other surface of the first adhesive layer 251 away from the first substrate layer 252 is provided on the first diaphragm 231. The thickness of the first adhesive layer 251 is H2, 2μm≤H2≤7μm, and the thickness of the first substrate layer 252 is H3, 8μm≤H3≤13μm. The first adhesive layer 251 can improve the adhesion of the first insulating layer 25 to the first diaphragm 231, and the first substrate layer 252 can improve the anti-puncture performance of the first insulating layer 25. By limiting 2μm≤H2≤7μm, the first adhesive layer 251 has a better bonding effect, and the first adhesive layer 251 will not be too thick, so as not to excessively reduce the energy density of the secondary battery 100. By limiting 8 μm≤H3≤13 μm, the first substrate layer 252 has a better insulation effect, while the first substrate layer 252 is not too thick, thereby not excessively reducing the energy density of the secondary battery 100 .

[0068] In some embodiments, the first adhesive layer 251 includes at least one of propylene oxide, polymethyl methacrylate and styrene-butadiene rubber, so that the first adhesive layer 251 has a better bonding effect. And / or, the first substrate layer 252 includes at least one of polyimide, polyethylene terephthalate, polypropylene and polyethylene, so that the first substrate layer 252 has a better anti-puncture performance.

[0069] In some embodiments, along the second direction Y, please refer to Figure 2 and Figure 4 , the width of the first welding area 24a is W2, 0.8mm≤W2≤3mm. By limiting 0.8mm≤W2, the first welding area 24a has good welding strength, so that the first conductive member 24 can be firmly attached to the first positive electrode current collector 2111. Since the first insulating layer 25 needs to shield the first welding area 24a, if the width of the first welding area 24a increases, the width of the corresponding first insulating layer 25 also needs to increase. Therefore, by limiting W2≤3mm, the width of the first welding area 24a will not be too wide, and the width of the first insulating layer 25 will not be too wide, so as not to excessively reduce the energy density of the secondary battery 100.

[0070] In some embodiments, 6.5 mm≤L2≤15.5 mm, so that the first conductive member 24 and the first positive electrode current collector 2111 have a good connection strength, while the first conductive member 24 is not too long, thereby not excessively reducing the energy density of the secondary battery 100.

[0071] In some embodiments, the first separator 231 includes a fifth portion 231a and a sixth portion 231b connected in sequence along the second direction Y. Along the first direction X, the projection of the fifth portion 231a on the surface of the negative electrode sheet 22 overlaps with the first negative electrode active layer 222. Along the second direction Y, the sixth portion 231b exceeds the first negative electrode active layer 222, and the width of the sixth portion 231b is W4, 0.5mm≤W4≤2mm. By limiting 0.5mm≤W4, the sixth portion 231b of the first separator 231 can shield the first negative electrode active layer 222, reducing the possibility of the first negative electrode active layer 222 contacting the first conductive member 24 and short-circuiting. By limiting W4≤2mm, the sixth portion 231b of the first separator 231 will not be too wide, and the energy density of the secondary battery 100 will not be reduced too much.

[0072] In some embodiments, the first positive electrode active layer 2112 includes a seventh portion 211c and an eighth portion 211d, and the eighth portion 211d is connected to the side of the seventh portion 211c close to the first conductive member 24 along the second direction Y. Along the first direction X, the maximum thickness of the eighth portion 211d is less than the minimum thickness of the seventh portion 211c, and the projection of the first insulating layer 25 on the surface of the single-sided positive electrode sheet 211 overlaps at least part of the eighth portion 211d. The first positive electrode active layer 2112 will form a torque during the cold pressing process. By limiting the maximum thickness of the eighth portion 211d of the first positive electrode active layer 2112 to be less than the minimum thickness of the seventh portion 211c, the thinner eighth portion 211d can buffer the torque to reduce the possibility of the first positive current collector 2111 being torn due to the torque. Since the eighth portion 211d is relatively thin, by limiting the projection of the first insulating layer 25 on the surface of the single-sided positive electrode sheet 211 to overlap at least part of the eighth portion 211d, the thickness of the electrode assembly 20 along the first direction X will not be increased too much, and the possibility of the first insulating layer 25 shielding the first welding area 24a can be further improved. In some embodiments, the thickness of the eighth portion 211d gradually decreases from the seventh portion 211c to the eighth portion 211d, so that the eighth portion 211d can better buffer the torque force.

[0073] In some embodiments, please refer to Figure 6 , Figure 7 and Figure 8The positive electrode sheet 21 includes a single-sided positive electrode sheet 212, and a single-sided positive electrode sheet 212 is disposed between two adjacent negative electrode sheets 22 along the first direction X. The single-sided positive electrode sheet 212 includes a second positive electrode collector 2121 and a second positive electrode active layer 2122. The second positive electrode collector 2121 includes a ninth portion 212a and a tenth portion 212b connected in sequence along the second direction Y. The second positive electrode active layer 2122 is disposed on both opposite surfaces of the ninth portion 212a along the first direction X, and the second positive electrode active layer 2122 is not disposed on both opposite surfaces of the tenth portion 212b along the first direction X. The second positive electrode collector 2121 includes a second metal layer 2123 and a second polymer layer 2124, and the second metal layer 2123 is disposed on both opposite surfaces of the second polymer layer 2124 along the first direction X. The second conductive member 26 is welded to both opposite surfaces of the tenth portion 212b along the first direction X, and a second welding area 26a is formed. The diaphragm 23 includes a second diaphragm 232, and the second diaphragm 232 is disposed between the single-sided positive electrode sheet 212 and the negative electrode sheet 22. A second insulating layer 27 is disposed on one surface of the second diaphragm 232 facing the single-sided positive electrode sheet 212, and the projection of the second insulating layer 27 on the surface of the single-sided positive electrode sheet 212 along the first direction X covers the second welding area 26a. The single-sided positive electrode sheet 212 is disposed between two adjacent negative electrode sheets 22 along the first direction X, and the second positive active layer 2122 is disposed on both opposite surfaces of the second positive electrode collector 2121 of the single-sided positive electrode sheet 212, so that the number of layers of the second positive electrode collector 2121 can be reduced, thereby improving the energy density of the secondary battery 100. By setting the second positive electrode collector 2121 as a structure in which two layers of the second metal layer 2123 sandwich the second polymer layer 2124, the second metal layer 2123 can be made thinner, thereby improving the energy density of the secondary battery 100. The second conductive member 26 is welded on both opposite surfaces of the tenth portion 212b of the second positive electrode collector 2121 along the first direction X, so that the positive electrode tab is conveniently connected to the second positive electrode collector 2121 through the second conductive member 26. The second insulating layer 27 is provided on a surface of the second separator 232 facing the single-sided positive electrode sheet 212, and the projection of the second insulating layer 27 on the surface of the single-sided positive electrode sheet 212 along the first direction X covers the second welding area 26a, so that the second insulating layer 27 can block the metal burrs of the second welding area 26a, thereby reducing the possibility that the metal burrs of the second welding area 26a pierce the second separator 232 and form a short circuit with the negative active material layer of the opposite negative electrode sheet 22. The second conductive member 26 may include at least one of aluminum, copper, nickel, titanium, and silver.

[0074] In some embodiments, the second polymer layer 2124, as the main mechanical support layer of the second positive electrode current collector 2121, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), and the second metal layer 2123 may include at least one of aluminum, copper, nickel, titanium, and silver. The second positive electrode active layer 2122 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The second positive electrode active layer 2122 includes a second positive electrode active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated on the opposite surfaces of the ninth part 212a of the second positive electrode current collector 2121 along the first direction X, thereby obtaining the second positive electrode active layer 2122. The second positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0075] In some embodiments, along the third direction Z, the length of the second insulating layer 27 is L3, the width of the second conductive member 26 is L4, 1mm≤L3-L4≤6mm, and by limiting 1mm≤L3-L4, the second insulating layer 27 can better shield the metal burrs of the second welding area 26a. Since the second insulating layer 27 is too long and easy to fold, thereby affecting its effect of shielding the second welding area 26a, by limiting L3-L4≤6mm, the length of the second insulating layer 27 will not be too long, thereby reducing the possibility of the second insulating layer 27 folding, thereby further improving the possibility of the second insulating layer 27 shielding the metal burrs of the second welding area 26a.

[0076] In some embodiments, along the third direction Z, the second conductive member 26 includes a third curved portion 262 and a second main body 261 connected in sequence, and the second insulating layer 27 exceeds the side of the third curved portion 262 away from the second main body 261, and the length of the excess is 0.5mm to 3mm. Torque will be formed during the die-cutting process of the second conductive member 26, and the third curved portion 262 can buffer the torque to reduce the possibility of the second positive electrode current collector 2121 being torn due to the torque. Since the length of the second insulating layer 27 is limited by the processing accuracy, by limiting the second insulating layer 27 to exceed the side of the third curved portion 262 away from the second main body 261, and the excess length is not less than 0.5mm, it can be satisfied that the second insulating layer 27 can better shield the metal burrs of the second welding area 26a, while giving the second insulating layer 27 a larger processing accuracy space. By limiting the second insulating layer 27 to extend beyond the third curved portion 262 and away from the second main body portion 261 and with the length of the extension being no more than 3 mm, the possibility of the second insulating layer 27 being too long and easy to fold can be reduced, as well as the possibility of the second insulating layer 27 being too long and consuming more energy density of the secondary battery 100 can be reduced.

[0077] In some embodiments, the second conductive member 26 includes a fourth bend 263, along the third direction Z, the fourth bend 263 is connected to the side of the second main body 261 away from the third bend 262, and the second insulating layer 27 exceeds the side of the fourth bend 263 away from the second main body 261, and the length of the excess is 0.5mm to 3mm. The fourth bend 263 can buffer the torque force of the die-cutting process to further reduce the possibility of the second positive electrode current collector 2121 being torn due to the torque force. By limiting the second insulating layer 27 to exceed the side of the fourth bend 263 away from the second main body 261, and the excess length is not less than 0.5mm, the second insulating layer 27 can be given a larger processing accuracy space while satisfying that the second insulating layer 27 can better shield the metal burrs of the second welding area 26a. By limiting the second insulating layer 27 to extend beyond the fourth curved portion 263 and away from the second main body portion 261 and with the excess length being no more than 3 mm, the possibility of the second insulating layer 27 being too long and easy to fold can be reduced, as well as the possibility of the second insulating layer 27 being too long and consuming more energy density of the secondary battery 100 can be reduced.

[0078] In some embodiments, along the second direction Y, the width of the second insulating layer 27 is W5, 1.4 mm ≤ W5 ≤ 4 mm, so that the second insulating layer 27 can well shield the metal burrs of the second welding area 26a, while the second insulating layer 27 is not too wide, and the energy density of the secondary battery 100 is not excessively lost. Along the first direction X, the thickness of the second insulating layer 27 is H4, 10 μm ≤ H4 ≤ 20 μm. So that the second insulating layer 27 can meet the requirements of good anti-puncture performance, while the second insulating layer 27 is not too thick, and the energy density of the secondary battery 100 is not excessively lost.

[0079] In some embodiments, please refer to Figure 6 and Fig. 9The second insulating layer 27 includes a second adhesive layer 271 and a second substrate layer 272. Along the first direction X, the second adhesive layer 271 has a second substrate layer 272 disposed on one surface thereof, and the second adhesive layer 271 is disposed on the second diaphragm 232 on the other surface thereof away from the second substrate layer 272. The thickness of the second adhesive layer 271 is H5, 2μm≤H5≤7μm, and the thickness of the second substrate layer 272 is H6, 8μm≤H6≤13μm. The second adhesive layer 271 can improve the adhesion between the second insulating layer 27 and the second diaphragm 232, and the second substrate layer 272 can improve the puncture resistance of the second insulating layer 27. By limiting 2μm≤H5≤7μm, the second adhesive layer 271 has a better adhesion effect, and the second adhesive layer 271 will not be too thick, thereby not excessively reducing the energy density of the secondary battery 100. By limiting 8 μm≤H6≤13 μm, the second substrate layer 272 has a better insulation effect while the second substrate layer 272 is not too thick, thereby not excessively reducing the energy density of the secondary battery 100 .

[0080] In some embodiments, the second adhesive layer 271 includes at least one of propylene oxide, polymethyl methacrylate and styrene-butadiene rubber, so that the second adhesive layer 271 has a better bonding effect. And / or, the second substrate layer 272 includes at least one of polyimide, polyethylene terephthalate, polypropylene and polyethylene, so that the second substrate layer 272 has a better anti-puncture performance.

[0081] In some embodiments, please refer to Figure 6 and Figure 8 , along the second direction Y, the width of the second welding area 26a is W6, 0.8mm≤W6≤3mm. By limiting 0.8mm≤W6, the second welding area 26a has good welding strength, so that the second conductive member 26 can be firmly attached to the second positive electrode current collector 2121. Since the second insulating layer 27 needs to shield the second welding area 26a, if the width of the second welding area 26a increases, the width of the corresponding second insulating layer 27 also needs to increase. Therefore, by limiting W6≤3mm, the width of the second welding area 26a will not be too wide, and the width of the second insulating layer 27 will not be too wide, so as not to excessively reduce the energy density of the secondary battery 100.

[0082] In some embodiments, 6.5 mm≤L4≤15.5 mm, so that the second conductive member 26 and the second positive electrode current collector 2121 have a good connection strength, while the second conductive member 26 is not too long, thereby not excessively reducing the energy density of the secondary battery 100.

[0083] In some embodiments, the electrode assembly 20 satisfies at least one of the following conditions: (1) the first metal layer 2113 includes aluminum. (2) the first polymer layer 2114 includes polyolefin. (3) the first conductive member 24 includes aluminum. (4) the first insulating layer 25 includes polyolefin.

[0084] In the second aspect of the present application, an electronic device is also proposed, including a secondary battery 100 as in any embodiment of the first aspect described above. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices include but are not limited to Bluetooth headsets, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys, electric airplane toys, and the like, and spacecraft can include airplanes, rockets, space shuttles, spacecraft, and the like.

[0085] In the third aspect of the present application, a manufacturing method of a secondary battery 100 is also proposed, which is used to prepare a secondary battery 100 as any embodiment of the first aspect, comprising: providing a negative electrode sheet 22, a separator 23 and a single-sided positive electrode sheet 212, and stacking the separator 23, the negative electrode sheet 22, the separator 23 and the single-sided positive electrode sheet 212 in sequence along the first direction X to form a first component, wherein the outermost electrode sheet of the first component along the first direction X is the negative electrode sheet 22, and the outermost layer of the first component along the first direction X is stacked with a first separator 231. Providing a first insulating layer 25, and setting the first insulating layer 25 on a surface of the first separator 231 of the first component away from the negative electrode sheet 22 to form a second component. Providing a single-sided positive electrode sheet 211 and a first conductive member 24, welding the first conductive member 24 to the opposite surfaces of the second part 211b of the first positive electrode collector 2111 of the single-sided positive electrode sheet 211, and forming a first welding area 24a. The single-sided positive electrode sheet 211 welded with the first conductive member 24 is stacked on the two opposite surfaces of the second assembly along the first direction X, wherein the projection of the first insulating layer 25 on the surface of the single-sided positive electrode sheet 211 along the first direction X covers the first welding area 24a. Through the above manufacturing method, when the diaphragm 23 of the middle layer of the electrode assembly 20 is not provided with an insulating layer, it is not necessary to first bond the diaphragm 23 to the insulating layer and then roll it up before stacking the electrode sheet, thereby reducing the possibility that the diaphragm 23 is difficult to roll up after being bonded to the insulating layer, and reducing the possibility that the diaphragm 23 will bulge and tear after being bonded to the insulating layer and rolled up.

[0086] Test part:

[0087] 1. Energy density improvement test of lithium-ion batteries:

[0088] Energy density calculation method: Use the glue-sticking solution to overlap the roll welding and the tape on the thickness of the battery cell to protect the junction between the positive electrode ear and the negative electrode. The insulating ceramic layer coating on the edge of the positive electrode can be cancelled. Compared with the coating of the ceramic layer + roll welding process, the energy density is improved at the expense of the reduction in the head space. The calculation logic is: Energy density improvement = (ceramic layer width + roll welding width - glue-sticking and roll welding overlapping width) / battery cell length * 100%.

[0089] 2. Drop test:

[0090] In the 20±5 test environment, use a metal drop floor to drop from a height of 1.8m along the head and tail once, and drop once at the four corners, for a total of 7 rounds of testing. The drop order is (head->tail->right corner of the head->right corner of the tail->left corner of the head->left corner of the tail (angle: 45±15 degrees, 6 times per round)); judgment criteria: no fire, no explosion, no smoke, and no leakage.

[0091] 3. Adhesive tape folding test:

[0092] The folding of the adhesive tape can be directly visually identified on the lamination equipment, and the corresponding data can be directly presented on the production site. The calculation logic is: adhesive tape folding ratio = adhesive tape folded pole piece / total number of pole pieces*100%.

[0093] Example 1

[0094] <Preparation of positive electrode sheet>:

[0095] The positive electrode active materials lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, which is then stirred evenly.

[0096] Polyethylene terephthalate is selected as the polymer layer, and two metal layers of aluminum are evaporated on the two surfaces of the polymer layer to obtain a positive current collector. The above slurry is coated on the surface of the metal layer of the positive current collector and a positive empty foil section is reserved. The slurry is dried to obtain a single-sided positive electrode sheet coated with a positive electrode active material layer on one side. On the other metal layer, the above steps are repeated to obtain a double-sided positive electrode sheet coated with a positive electrode active material layer on both sides.

[0097] <Preparation of negative electrode sheet>:

[0098] Using graphite as the negative electrode active material, the negative electrode active material graphite, the binder styrene butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, a slurry with a solid content of 70wt% is prepared, and the slurry is stirred evenly.

[0099] Polyethylene terephthalate is selected as the polymer layer, and two metal layers of copper are respectively evaporated on the two surfaces of the polymer layer. The above slurry is coated on the surface of one metal layer and a negative electrode empty foil section is reserved. The slurry is dried to obtain a single-sided composite negative electrode sheet coated with a negative electrode active material layer on one side. On the other metal layer, the above steps are repeated to obtain a double-sided composite negative electrode sheet coated with a negative electrode active material layer on both sides.

[0100] <Preparation of diaphragm>:

[0101] A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramics and a PVDF binder is coated on one surface of the substrate layer as a diaphragm (CCS), wherein the mass percentage of the alumina ceramics in the ceramic layer is 95%.

[0102] <Electrolyte Preparation>:

[0103] In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0104] <Preparation of ceramic layer>:

[0105] In the production of battery cells, the ceramic layer is prepared in the coating process. The insulating ceramic layer slurry and the positive electrode active material slurry are introduced into the extrusion mechanism together. The position, size and weight of the slurry are set through the extrusion coating opening at different positions in different slurry strips in the extrusion coating machine (the ceramic layer is conventionally coated on the edge of the positive electrode active material, and the two have a certain interaction area, which needs to be specially defined. In the interaction area, the ceramic layer is at the top away from the current collector, and the active material layer is at the bottom close to the current collector) to obtain a positive electrode sheet with a ceramic layer. The thickness of the ceramic layer is 25μm.

[0106] <Preparation of adhesive tape>:

[0107] Preparation process of adhesive tape: first prepare polypropylene glue, take polypropylene ancient costume glue, heat it to 160-190℃ to make it completely liquefied; then apply the glue on two layers of release film (one layer of complete release film, one layer of release film with grooves, put the complete release film on the lower layer, apply the glue in the empty groove of the second layer of release film, and then scrape off the excess glue with a scraper to make the surface of the adhesive tape flat), cool and solidify to obtain adhesive tape with release film. The thickness of the adhesive tape is 15μm.

[0108] <Preparation of lithium-ion batteries>:

[0109] A conductive member made of aluminum is welded to the empty foil section of the double-sided positive electrode sheet with a ceramic layer next to the ceramic layer. The double-sided positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence to form a preliminary electrode assembly. The adhesive tape is pasted on the surface of the outermost separator of the preliminary electrode assembly away from the negative electrode sheet, corresponding to the positive and negative electrode intersection area below the negative electrode ear, and the conductive member made of aluminum is welded to the empty foil section of the single-sided positive electrode sheet. The single-sided positive electrode sheet is stacked on the outermost layer of the preliminary electrode assembly, and the adhesive tape of the separator covers the weld mark of the conductive member of the single-sided positive electrode sheet to form the final electrode assembly. The final electrode assembly is hot pressed. The final electrode assembly is placed in the aluminum-plastic film of the packaging bag, injected with electrolyte and packaged to obtain a lithium-ion battery.

[0110] The relevant parameters in Comparative Examples 1 to 8 and Examples 2 to 17 are shown in Table 1 below.

[0111] Among them, in Comparative Examples 1 to 3, ceramic layers are only provided on the empty foil segments of all positive electrode current collectors, and adhesive tape is not provided on the separator.

[0112] In Comparative Examples 4 to 6, only adhesive tape is provided on all positive electrode conductive parts, and no ceramic layer is provided on the empty foil section of the positive electrode current collector, and no adhesive tape is provided on the separator.

[0113] Comparative Examples 7 to 8 and Examples 7 to 17 only set adhesive tape on the diaphragms corresponding to all positive electrode conductive parts, and no ceramic layer is set on the empty foil section of the positive electrode current collector. Among them, Comparative Examples 7 to 8 and Examples 7 to 9 only differ in the length of the part of the diaphragm set adhesive tape that exceeds the width of the conductive part. Examples 10 to 13 only differ in the width of the diaphragm set adhesive tape. Examples 14 to 17 only differ in the thickness of the diaphragm set adhesive tape.

[0114] In Examples 1 to 3, adhesive tape is disposed on the single-sided positive electrode conductive member corresponding to the separator, and a ceramic layer is disposed on the empty foil section of the double-sided positive electrode current collector, and only the width of the ceramic layer is different.

[0115] In Examples 4 to 6, adhesive tape is set on the single-sided positive electrode conductive member corresponding to the diaphragm, and adhesive tape is set on the double-sided positive electrode conductive member, and only the length of the portion of the diaphragm where the adhesive tape is set that exceeds the width of the positive electrode conductive member is different.

[0116] The step of providing adhesive tape on the positive electrode conductive member in the above-mentioned comparative examples 4 to 6 and embodiments 4 to 6 is: sticking the adhesive tape on the surface of the conductive member of the positive electrode plate and covering the welding area of ​​the conductive member.

[0117] It should be explained that the length of the portion of the adhesive tape on one side of the separator that exceeds the width of the positive electrode conductive member refers to the length of the portion of the adhesive tape that exceeds the width of the positive electrode conductive member on any one of the two sides in the width direction of the positive electrode conductive member. Similarly, the length of the portion of the adhesive tape that exceeds the width of the conductive member on the positive electrode conductive member refers to the length of the portion of the adhesive tape that exceeds the width of the positive electrode conductive member on any one of the two sides in the width direction of the positive electrode conductive member.

[0118] Table 1

[0119]

[0120]

[0121] Note: “ / ” in Table 1 means that the parameter is not included.

[0122] According to the above Table 1, combined with Comparative Examples 1 to 6 and Examples 7 to 9, it can be known that by setting a ceramic layer on the current collector so that the welding area of ​​the conductive part and the current collector protrudes from the opposite active material layer of the opposite polarity in the length and / or width direction of the current collector, the battery cell can obtain a good drop test pass rate, that is, the risk of battery cell short circuit can be improved well, but this method excessively loses the energy density of the battery cell. By setting adhesive tape covering the welding area on the conductive part, the risk of battery cell short circuit can be improved well, and the energy density of the battery cell will not be excessively lost. However, this method has the problem of reducing the manufacturing rate of the pole piece, causing the active material particles near the conductive part to fall off, and reducing production efficiency. By setting adhesive tape on the conductive part corresponding to the diaphragm, the risk of battery cell short circuit can be improved well, and the energy density of the battery cell will not be excessively lost. In actual applications, the diaphragm is set with adhesive tape, which can better improve the problems of low manufacturing rate of pole pieces, falling off of active material particles and low production efficiency compared with the conductive part.

[0123] Combining Comparative Examples 7 to 8 and Examples 7 to 9, it can be seen that when the length of the conductive part corresponding to the diaphragm setting adhesive tape on one side exceeds the width of the conductive part by more than 3mm, that is, the sum of the lengths of the two sides of the adhesive tape exceeding the width of the conductive part is greater than 6mm, the adhesive tape is folded at a large ratio, thereby affecting the adhesive tape from shielding the conductive part welding area. In practical applications, when the length of the conductive part corresponding to the diaphragm setting adhesive tape on one side exceeds the width of the conductive part by less than 0.5mm, that is, the sum of the lengths of the two sides of the adhesive tape exceeding the width of the conductive part is less than 1mm, the adhesive tape cannot well shield the conductive part welding area. Therefore, it is necessary to limit the sum of the lengths of the conductive part corresponding to the diaphragm setting adhesive tape on both sides exceeding the width of the conductive part to 1mm to 6mm.

[0124] In combination with Examples 10 to 13, it can be seen that when the width of the adhesive tape set for the conductive part corresponding to the diaphragm is greater than 4 mm, the energy density of the battery cell will be excessively consumed. In actual applications, when the width of the adhesive tape set for the conductive part corresponding to the diaphragm is less than 1.4 mm, the adhesive tape cannot effectively cover the welding area of ​​the conductive part. Therefore, it is necessary to limit the width of the adhesive tape set for the conductive part corresponding to the diaphragm to 1.4 mm to 4 mm.

[0125] In combination with Examples 14 to 17, it can be seen that when the thickness of the tape set for the conductive part corresponding to the diaphragm is less than 10μm, the pass rate of the battery cell drop test is low. In actual applications, when the thickness of the tape set for the conductive part corresponding to the diaphragm is greater than 20μm, the energy density of the battery cell will be excessively consumed. Therefore, the thickness of the tape set for the conductive part corresponding to the diaphragm needs to be limited to 10μm to 20μm.

[0126] From Comparative Examples 1 to 3 and Examples 1 to 3, it can be seen that, compared with setting a ceramic layer for all positive electrode current collectors, only the positive electrode current collector of the outermost single-sided positive electrode sheet is freed from the ceramic layer, and instead the positive electrode conductive member is provided with adhesive tape corresponding to the diaphragm, so that the battery cell can obtain a good drop test pass rate. At the same time, in actual applications, the positive electrode current collector of the outermost single-sided positive electrode sheet is freed from the ceramic layer, which can slightly increase the energy density of the battery cell.

[0127] Combining comparative examples 4 to 6 and embodiments 4 to 6, it can be seen that compared with setting adhesive tape on all positive electrode conductive parts, only the conductive parts of the outermost single-sided positive electrode sheet are freed from adhesive tape, and adhesive tape is set on the positive electrode conductive parts corresponding to the diaphragm instead, which can also enable the battery cell to obtain a good drop test pass rate and a good energy density.

[0128] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly comprises a negative electrode sheet, a positive electrode sheet and a separator, wherein the negative electrode sheets and the positive electrode sheets are alternately stacked along a first direction, and the separator is disposed between adjacent negative electrode sheets and positive electrode sheets; The positive electrode sheet comprises a single-sided positive electrode sheet, the outermost electrode sheet of the electrode assembly along the first direction is the single-sided positive electrode sheet, the single-sided positive electrode sheet comprises a first positive electrode current collector and a first positive electrode active layer, the first positive electrode current collector comprises a first part and a second part connected in sequence along the second direction, the first part is provided with the first positive electrode active layer on a surface facing the negative electrode sheet, and the second part is not provided with the first positive electrode active layer on two opposite surfaces along the first direction; the first positive electrode current collector comprises a first metal layer and a first polymer layer, and the first polymer layer is provided with the first metal layer on two opposite surfaces along the first direction; It is characterized in that The first conductive member is welded to both opposite surfaces of the second part along the first direction to form a first welding area; the first conductive member protrudes from the second part along the second direction; the diaphragm includes a first diaphragm, the first diaphragm is arranged between the single-sided positive electrode sheet and the adjacent negative electrode sheet, the first diaphragm is arranged on the surface facing the single-sided positive electrode sheet, and the projection of the first insulating layer on the single-sided positive electrode sheet along the first direction covers the first welding area; Along the third direction, the first insulating layer exceeds one side of the first conductive component, and the exceeding length is 0.5 mm to 3 mm. The first direction, the second direction and the third direction are perpendicular to each other.

2. The secondary battery according to claim 1, characterized in that: Along the third direction, the first conductive member includes a first bent portion and a first main body portion connected in sequence, and the first insulating layer extends beyond a side of the first bent portion away from the first main body portion, and the extending length is 0.5 mm to 3 mm.

3. The secondary battery according to claim 2, characterized in that: The first conductive member includes a second bent portion, and along the third direction, the second bent portion is connected to a side of the first main body away from the first bent portion, and the first insulating layer extends beyond the side of the second bent portion away from the first main body, and the length of the extension is 0.5 mm to 3 mm.

4. The secondary battery according to claim 1, characterized in that: Along the second direction, the width of the first insulating layer is W1, 1.4 mm≤W1≤4 mm.

5. The secondary battery according to claim 1, characterized in that: Along the first direction, the thickness of the first insulating layer is H1, 10 μm≤H1≤20 μm.

6. The secondary battery according to claim 1, characterized in that: The first insulating layer includes a first adhesive layer and a first substrate layer. Along the first direction, the first substrate layer is disposed on one surface of the first adhesive layer, and the other surface of the first adhesive layer facing away from the first substrate layer is disposed on the first diaphragm. The thickness of the first adhesive layer is H2, 2μm≤H2≤7μm, and the thickness of the first substrate layer is H3, 8μm≤H3≤13μm.

7. The secondary battery according to claim 1, characterized in that: Along the second direction, the width of the first welding area is W2, 0.8 mm≤W2≤3 mm.

8. The secondary battery according to claim 1, characterized in that: The length of the first conductive member along the third direction is L2, 6.5 mm≤L2≤15.5 mm.

9. The secondary battery according to claim 1, characterized in that: The negative electrode sheet comprises a first negative electrode current collector and a first negative electrode active layer, the first negative electrode current collector is provided with the first negative electrode active layer on at least one surface along the first direction, the first negative electrode active layer comprises a third portion and a fourth portion connected in sequence along the second direction, the projection of the third portion on the surface of the single-sided positive electrode sheet overlaps with the first portion, and the projection of the fourth portion on the surface of the single-sided positive electrode sheet overlaps with at least part of the second portion; Along the second direction, the width of the fourth portion is W3, 0.5 mm≤W3≤2 mm.

10. The secondary battery according to claim 9, characterized in that: The first diaphragm includes a fifth part and a sixth part connected in sequence along the second direction; along the first direction, the projection of the fifth part on the surface of the negative electrode sheet overlaps with the first negative electrode active layer; along the second direction, the sixth part exceeds the first negative electrode active layer, and the width of the sixth part is W4, 0.5mm≤W4≤2mm.

11. The secondary battery according to claim 1, characterized in that: The first positive electrode active layer includes a seventh part and an eighth part, and the eighth part is connected to the side of the seventh part close to the first conductive member along the second direction; along the first direction, the thickness of the eighth part is less than the thickness of the seventh part, and the projection of the first insulating layer on the surface of the single-sided positive electrode sheet overlaps with at least part of the eighth part.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The positive electrode sheet comprises a double-sided positive electrode sheet, the double-sided positive electrode sheet is arranged between two adjacent negative electrode sheets along the first direction, the double-sided positive electrode sheet comprises a second positive electrode current collector and a second positive electrode active layer, the second positive electrode current collector comprises a ninth part and a tenth part connected in sequence along the second direction, the second positive electrode active layer is arranged on both opposite surfaces of the ninth part along the first direction, and the second positive electrode active layer is not arranged on both opposite surfaces of the tenth part along the first direction, the second positive electrode current collector comprises a second metal layer and a second polymer layer, and the second metal layer is arranged on both opposite surfaces of the second polymer layer along the first direction; The tenth part has second conductive parts welded to two opposite surfaces along the first direction to form a second welding area; the diaphragm includes a second diaphragm, the second diaphragm is arranged between the double-sided positive electrode sheet and the negative electrode sheet, and the second diaphragm has a second insulating layer arranged on a surface facing the double-sided positive electrode sheet, and the projection of the second insulating layer on the surface of the double-sided positive electrode sheet along the first direction covers the second welding area.

13. The secondary battery according to any one of claims 1 to 11, characterized in that: The electrode assembly satisfies at least one of the following conditions: (1) The first metal layer includes aluminum; (2) The first polymer layer includes polyolefin; (3) The first conductive member includes aluminum; (4) The first insulating layer includes polyolefin.

14. An electronic device, characterized in that: Comprising the secondary battery as claimed in any one of claims 1 to 13.

15. A method for manufacturing a secondary battery, for preparing the secondary battery as claimed in any one of claims 1 to 13, characterized in that: include: Providing the negative electrode sheet, the separator and the double-sided positive electrode sheet, and stacking the separator, the negative electrode sheet, the separator and the double-sided positive electrode sheet in sequence along the first direction to form a first component, wherein the outermost electrode sheet of the first component along the first direction is the negative electrode sheet, and the outermost layer of the first component along the first direction is stacked with a first separator; Providing the first insulating layer, and disposing the first insulating layer on a surface of the first diaphragm of the first component away from the negative electrode sheet to form a second component; Providing the single-sided positive electrode sheet and the first conductive member, welding the first conductive member to two opposite surfaces of the second portion of the first positive electrode collector of the single-sided positive electrode sheet, and forming the first welding area; The single-sided positive electrode sheet welded with the first conductive member is stacked on two opposite surfaces of the second component along the first direction, wherein the projection of the first insulating layer on the surface of the single-sided positive electrode sheet along the first direction covers the first welding area.

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